Preparation of magnesium nitride



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Ill/111111 (IIIIIA CARRIER GAS (N J. L. PORTER PREPARATION OF Filed Jan. 2, 1945 MAGNESIUM NITRIDE IN VEN TOR.

Patented Nov. 8, 1949 Jlohnf. L. Porter;

Permanente Palo. Alto, Galizia. assignan'ta They I Metals Corporatiom.

Qakland,

Calif.,. a.. corporation of Delaware. Application January 2, 1945; Serial No. 57211,@74 7. Claims. (Cl. 23.--191),v

Thisr invention; relatesto processes for preparing magnesium nitride, and particularly to processes vwhereinmagnesium. is reactedwith nitrogen or` a.nitrogen-yielding; gas.4

Magnesium-- nitride.- reacts; very readily with Waiter to; ioum ain-momiav and it. isi evident4 thereforeV thatY the. compound1 is a: useuk dehydrating agent in inorganic reactions, and. is4 also useful in organicV syntheses It: is. also.` useful in compounding synthetic rubber., Anumber. of methods for. preparing; the magnesium. nitride: compound havefbeen reported ina the literaturebutextensive practical.preparationof` theproduct hasnot been knovvn.` The methods reportedA by various investigators have included heating finely divided metal in a stream of nitrogen;- in a. restrictedamount: of. air'v (thereby formingl thef oxide until availableoxygen has been used up., and, then orming nitride) decomposition, oi magnesium ferrocyanide- Withheat,. reaction of the'v nely divided metal With ammonia; and reduction` of KCN-or-KCNS by magnesium; llt hasbeerr found that-certain. disadvantages. attend each of thesemethods. For instancain burning the metal. in a restricted, amount of, air.y an undesirable; contamination. with magnesium. oxide; is obtained-y and, the.v nitride being. very reactive,. its purica tion. isimpracticable.` Also whenl iinely divided metal heretofore available has been reacted4 by passing nitrogen, on ammoniav gasA thereover at temperatures of 6 1o C.l to. 900?7 C. as has been described in the literature. it is found that. a re. fractor-y mixture orsolution of the. nitride. in the metallic magnesiuml is; obtained which isv usually a hard, dense, black mass.. Such amate rialisnot usable inthe same manner asthe purey nitride.

It, has. also` been. proposed to react magnesium withv nitrogen or. ammonia at, relatively lower temperatures, .that is, atirom aboutArOI).o toxabout 600.? C. butthishasprOVed tooslovvto be practicable-,inoperatingwith thev magnesium powdersA or turnings available. inA the.. prior art.. In. this reactionwhich. takes placebetvveen a gasY and. a. solid, theY directnitridingof relatively largey crystals or masses. ofthe metal does. notproceed. to` completion, perhaps because the magnesium. nitride formsT a hard; coating. over the surface ofthe metaL,effectivelyr protecting the inner po1.

tions from further attack by. the. nitriding gas.. Ithasiurther beenproposed to prepare.animi--k num or' magnesium nitride. by reducing. mag-L nesium oxidewith.acarbonaceous reducing agentV atfor example., 1.800?Y C..t o.22(10f C'.,.W1thdrawng. the gaseousproductsoi reaction (magnesium or nesiurn-k vapors-A above 1120? the nitrogenor, NH3 may be'V magnesium starting material.

" zone. ismaintained. at,

2 aluminum vapor and CO) to. a separate reaction zone, andi there; bringingthese products. intoi contact, withr nitrogen or a. nitrogen.-carryingY gas,

and; cooling. with'k formation; of nitride., Howeven;

magnesium vapor under these conditions prefer-- entially: reactsawiththe Oxygenv of the CO and very smallquantities ornitride. ara formed..l

reactions. involved. ing, this; system tend` to. prcniuce magnesium' oxide as; long as.y suiiici'ent oxygenA is; available to satisfyy the: magnesium, although',Y of course; some nitride may be; formed.

According t@ this invention it has; novv been. found that -n'iagnesiuml nitride can be: preparedv by bringing;` magnesium vapor intof contact with; a. nitrogenfyielding; stahtial proportion oi an oxygen-yielding,v gas. The nitrogenryieldingg gassuitablein this reaction. is nitrogen or ammonia, for example.. Preferably-, magnesium vapor attatemperatureof from about 909? C.,to abouti-120 gas Whichhas-,been pre-heatedl to atemperature ot atleast about. 400? C.. or withv ammonia gas pre-heated'. to at:1 least about 300 In someA cases itlmay be desirableto super-heat. the mag,-

C.. andVv in these cases the temperature.- oft somewhat lower than the-preferred values shown, butL in. nog casev must, this, temperature be low enoughv to cause depositionv of masses ofsolid metal without reaction to.Y nitride.

The magnesium vapor. is. advantageously ob-l tainedbyheating magnesium turnings, powdered magnesium, magnesium crystals,v the crude con'- densate or dust.- necovered:` by shock-chilling the vaporous` products. of reaction. issuing from the reduction zone ofthe carboth'ermie process for making magnesium. metal, or the like in aheating zoneL thev magnesiumL vapor beingVVK conducted thence toa reaction zone Contact with the nitrogen-yielding gas. The may also contain contaminants. asinthey case of. the. carbothermic condensate, for. example, which arev not volate` under` the conditions or operation.A

Flow of. magnesium. vapor, into. the reaction deposition., of. solid material in the connecting conduitsandto.-preventthereaction from traveling back. along thevapor stream. Sufficient ow may be. maintained. by developing magnesium vapor alone. in. the. vapor-ization zone, or in a variation the. flow, oi magnesium vapor can be supplemented with. a. carrier gas inert to. mag.- nesimn. andthe reactinggas under the` conditions. of'operation.

gas; in the? absence o a sub- C; isA reacted With nitrogen.

Where it is brought intoa. rate suflicient` to prevent.

removed from the heating zone even before the boiling point of magnesium is reached. The iiow of carrier gas varies with theitemperatureand vaporizing conditions of the furnace or heating zone. For example, when the vapor pressure of the magnesium is low, that is, at lower tempera-` reaction zone. The flow should not be sov fast, of course, that magnesium passes unreacted out of the reaction zone.

One of the important advantages of the process of this invention is that the reaction between the magnesium and the reacting gas is enabled to proceed to substantial completion. By the methods known to the art it has not been possible to produce magnesium nitride of controlled degree of purity. In those methods where solid metal, even divided as finely as possible by the comminuting processes available heretofore, has been reacted with a nitrogen-yielding gas the surface of the magnesium particle has reacted and thereby become coated with a hard and impervious layer of nitride and, as a result, a considerable amount of the metallic element has remained unreacted. In the method where a mixture of Mg vapor and CO 1s brought into contact with nimonoxide to give magnesium oxide and the yield of nitride has been negligible if perceptible at all. These disadvantages are overcome by the process of the present invention wherein magnesium is vaporized, conducted to a reaction Zone and there brought into contact with a nitrogen-yielding gas. In the absence of a substantial proportion of an oxygen-yielding gas, nitride is formed predominantly. That is to say, when the magnesium vapor is brought into contact with a nitrogenyielding gas in the presence of a proportion of available oxygen, magnesium oxide is formed until the oxygen supply is exhausted. The formation of nitride then begins. When it is desired to prepare highly pure nitride, the presence of available oxygen in the reaction zone is undesirable, but where a highly pure product is not required the presence of a small amount of oxygen is not objectionable. vBy using gases which are free of oxygen and moisture a substantially pure nitride is prepared.

The drawing illustrates an apparatus which is suitable for one method of carrying out the process of this invention. In the drawing, IU is the heating furnace which is preferably made of graphite blocks and contains annular heating space II into which magnesium, as in the form of magnesium crystals, is fed through a tube I2, suitably made of a glass section I3 and graphite section I4. Carrier gas, in this case hydrogen, is fed in at I 5 and acts to maintain a positive pressure along the path of travel of the crystals, preventing magnesium vapor from backing up and depositing in this line. If desired, the graphite inlet tube can also be heated, as by an electrical resistor coil. The graphite furnace I0 is heated duces nitrogen, or ammonia,

, heated toV aboutY 800 not exceeding 900 formed deposits as a fairly hard coating on theY by a globar element I6 which extends through a central conduit I7 which is sealed oi from the heating zone.

The vapors from graphite and is suitably heated by a resistor element I9 also. Gas ring 22 surrounds the area adjacent to entrance of tube I8 into reaction chamber 20 and introgas into intimate contact with the magnesium vapor stream. Inlet tube 23 for this gas, leading ably heated by an electrical resistor, to raise the temperature of the incoming gas to at least 300 to 400 C. and the temperature may preferably be raised to about 700 C. Ring 22 has apertures 2l on its inner face adapted to cause nitrogen, or-ammonia, gas to impinge directly on the magnesium vapor stream as it issues from tube I8.

Reaction chamber 2U can be made of steel or tion of the reaction by] means of resistors 24. It about outlet tube 26 which conducts the gases, comprising for purposes of i1- lustration hydrogen and excess nitrogen or excess ammonia, to removable top portion 21 whence the gases issue through tube 28. The issuing gas mixture may be separated and its component elements re-used, or it may be burned 01T. Within cap 2l is another baille device 29, which acts to product of reaction is removed from chamber 20, and from cap assembly 27.

In an example of the method of carrying out this invention, 3 grams of magnesium crystals per minute are fed to heating furnace I0 and at the Furnace I0 1s heated by globar element I6 to 1110 C. as measured by a thermocouple in well S0. Magnesium vapors flow by way of tube I3 to reaction chamber 20, which is C. to initiate the reaction, and as the vapors enter thereinto they are intimately mixed with a stream of nitrogen, preheated to 600 C., and entering through apertures in ring 22, the nitrogen being introduced at of reaction chamber 20 is discontinued, and the temperature is maintained close to 700 C. and C. The magnesium nitride walls and baiiles of the reaction chamber. removed by scraping and is a yellow granular solid, containing magnesium nitride, the remainder being magnesium oxide Aand magnesium hydroxide. AclvantageouslyV in this example, the

the reaction chamber. Excess gases pass oit through cap assembly 2'! which is at about 300 C., a further quantity of the nitride being recovered therein. y

In another example, 2 grams of magnesium crystals per minute areV added to the furnace I Il and hydrogen introduced at I5 at the rate of V3 liters per minute. The furnace is heated to 1090" C. and the mixture of magnesium vapor and hydrogen passes to reaction chamber 20 as in the example above. The reaction chamber is heated to 700 C. Ammonia gas, preheated to 600 C., is

introduced through ring 22 at the rate of 3 liters per minute. It reacts with the magnesium vapor to give a magnesium nitride which is a bright yellow powder and is very active.

If desired, a mixture of ammonia and nitrogen can be reacted with the magnesium vapor. Other carrier gases, such as helium, argon or the like can be used instead of hydrogen. Where large Volumes of vapors are treated and the heat of reaction tends to cause excessive rise of temperature in the reaction zone, the reaction zone is suitably cooled, as externally with cool gases or the like.

It is advantageous, in order to further the reaction and to increase the yield to the maximum, to maintain the reaction chamber at a temperature at which the magnesium and nitrogen-yielding gas have time to react, and at which magnesium metal evidently does not condense to a solid before it has reacted. It has been found that the reaction zone is preferably maintained at a temperature of from about 400 C. to about 1000 C. when the reacting gas is ammonia, and preferably from about 600 C. to about 1000 C. when the reacting gas is nitrogen. Similarly, the temperature of the incoming reactant gas, e. g. nitrogen or ammonia, is preferably just high enough to prevent condensation of magnesium to the solid metal before reaction occurs. Thus when the reaction zone is at a relatively higher temperature and the flow of magnesium vapor is relatively slightly slower, the temperature of the incoming reacting gas may be relatively less.

In the appended claims, the term oxygenproviding" gas is intended to mean a gas containing oxygen available for reaction with the magnesium vapor, including gases containing free oxygen for example, air, and gases containing combined oxygen, for example, carbon monoxide.

What is claimed is:

1. Process for making magnesium nitride which comprises heating and vaporizing magnesium metal, conducting said vaporized magnesium in the presence of an inert carrier gas into a reaction zone and there intimately admixing it with a gas at a temperature of at least 300 C., chosen from the group consisting of nitrogen and ammonia, and collecting the substantially pure magnesium nitride produced, the process being conducted in the absence of an s.

2. Process for making magnesium nitride which comprises heating and vaporizing magnesium metal in the presence of an inert gas, continuously conducting said vaporized magnesium and admixed inert gas to a reaction zone, said mixed vapors having a temperature of from about 900 C. to about 1120 C., intimately admxing said Longmans, London,

mixed vapors in said reaction zone with a continuous flow of nitrogen heated to a temperature of at least about 400 C., and collecting the substantially pure magnesium nitride produced, said process being conducted in the absence of an oxygen-yielding gas.

3. Process as in claim 2 wherein the inert gas is hydrogen. 2

4. Proces-s for making magnesium nitride which comprises heating and vaporizing magnesium metal in the presence of an inert gas, continuously conducting said Vaporized magnesium and admixed inert gas to a reaction zone, said mixed vapors having a temperature of from about 900 C. to about 1120 C., intimately mixing said mixed vapors in said reaction zone with a continuous flow of ammonia heated to at least about 300 C., and collecting the substantially pure magnesium nitride produced, said process being conducted in the absence of an oxygen-yielding gas.

5. Process as in claim 4' wherein the inert gas is hydrogen.

6. In a process for making magnesium nitride the steps which comprise heating and vaporizing magnesium, conducting vaporized magnesium in the presence of an inert carrier gas into a reaction zone maintained at a temperature of from about 600 C. to about 1000 C., and there intimately admixing it with a flow of nitrogen at a temperature of at least 400 C., said process being conducted in the absence of an oxygen-yielding gas.

7. In a process for making magnesium nitride the steps which comprise heating and vaporizing magnesium, conducting saidvaporized magnesium in the presence of an inert carrier gas into a reaction Zone maintained at a temperature of from about 600 C. to about 1000 C., and there intimately admixing it with a flow of ammonia at a temperature of at least 300 C., said process being conducted in the absence of an oxygen-yielding gas.

JOHN L. PORTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,803,720 Miner May 5, 1931 OTHER REFERENCES Mellor, Inorganic and Theoretical Chemistry,"

vol. VIII (1928), pp. 104, 105. Chemical Engineers Handbook, 2nd ed., Mc- Graw-Hill Book Co., New York (1941) page 339. 

